Complete loss of BRCA1/2 function is related to the sensitivity of DNA damaging drugs and treatment response. However not every tumor with LOH (loss of heterozygosity) in BRCA1/2 has significant response to DNA damaging drugs. An analysis has been conducted on 160 tumor samples with BRCA1/2 germline mutations from 100 breast and ovarian cancer patients. In this study, ovarian cancer patients with specific LOH site treated with platinum chemotherapies have lower overall survival rate and poor treatment response. Therefore, LOH could be a kind of reference to evaluate the effectiveness of DNA damaging drugs for patients with germline locus-specific LOH in BRCA1/2.